Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$131.25	6.315%	$139.5384	$139.54	$139.55	$139.50
Purchase #2	$147.77	12.832%	$166.7318	$166.73	$166.75	$166.70
Purchase #3	$220.66	12.807%	$248.9199	$248.92	$248.90	$248.90
Purchase #4	$132.86	6.394%	$141.3551	$141.36	$141.35	$141.40
Purchase #5	$176.35	11.569%	$196.7519	$196.75	$196.75	$196.80
Purchase #6	$167.32	6.571%	$178.3146	$178.31	$178.30	$178.30
Purchase #7	$188.54	6.524%	$200.8403	$200.84	$200.85	$200.80
7 purchase totals =	$1,164.75		$1,272.4520	$1,272.45	$1,272.45	$1,272.40